This invention relates to a method for manufacturing a heating furnace to be used when a thin film, such as silicon semiconductor single crystal thin films, is deposited on a surface of a wafer such as silicon semiconductor single crystal substrates.
For a deposition of a thin film such as a silicon semiconductor single crystal thin film on a surface of a wafer such as a silicon semiconductor single crystal substrate, there has been employed a so-called lamp heating furnace using radiant heating which is equipped with a light source for radiating light for use of heating, a lamp house having a wall surface that reflects light derived from the light source, and the like.
FIG. 1 shows an example of the arrangement of the heating furnace. This heating furnace comprises a reaction furnace 14 made of quartz glass 15 for holding a wafer 1 therein, and a lamp house 10 provided above the reaction furnace 14 and having a light source 11 such as a plurality of infrared lamps placed therein. The lamps of the light source 11 are arranged circumferentially in a plural number, and a mirror reflecting plate 12 for reflecting light emitted from the lamps of the light source 11 is mounted on the inside-wall surface of the lamp house 10. Besides, as required, a mirror reflecting cylinder 13 whose inner and outer surfaces depicted by broken line are mirror surfaces is also mounted. This mirror reflecting cylinder 13, which is removable, can be mounted for the control of heating distribution based on heating calculations.
Conventionally, design and manufacture of such a heating furnace has been carried out in a manner in which trials and errors are iterated through steps of, with respect to a trial-manufactured heating furnace prototype, first, measuring a heating temperature distribution of a wafer 1 in a heating experiment using thermocouples 2 as shown in FIG. 1, then making improvements on the heating furnace prototype based on results of the experiment, and further performing temperature measurement again in another heating experiment. In brief, the heating furnace has hitherto been designed and manufactured empirically. As a result, quite a large number of times of trials and errors have been involved before the completion.
This being the case, an attempt to reduce the number of times of trials and errors has also been made by performing temperature prediction with numerical calculation. This attempt is implemented by simulations based on the presumption that light emitted from the light source is all irregularly reflected.
However, since a mirror-surfaced reflecting plate has been used in recent years as the wall surface of the lamp house of the heating furnace for heating the wafer, such as a silicon semiconductor single crystal substrate, correct temperature predictions cannot be achieved without regarding the light reflection occurring at the wall surface of the lamp house as regular reflection, i.e., mirror reflection rather than irregular reflection. Besides, since the wafer to be heated is a mirror-surfaced wafer, the main surface of which has been mirror finished, there is a need for taking into consideration about the light reflection occurring at the wafer surface. Therefore, with such a simulation method as would be applied to a conventional heating furnace comprising radiant heating and an irregularly reflecting plate, it has been difficult to perform temperature prediction in the case where the mirror-surfaced wafer is heated by a heating furnace in which a mirror-surfaced reflecting plate is used as the mirror surface of the lamp house.
More specifically, in the heating process by the heating furnace of recent years' use, in which a mirror-surfaced wafer and a mirror reflecting plate are included as component members, light emitted from the light source imparts energy to the wafer while undergoing a great many number of times of reflections, thus making it difficult to predict the energy distribution on the wafer, unlike heating furnaces characterized principally by irregular reflection. Due to this, with simulations based on the assumption that all of light is irregularly reflected, insufficient prediction of temperature distribution or the like would result so that only a heating furnace low in the degree of completeness could be obtained. Thus, in order to solve such issues as low heating efficiency, excessive trials and errors would be involved inevitably. This would lead to losses of not only time and expense but also earth resources.